1. Field of the Invention
This invention relates to synthetic plastic drain pipe. More particularly, this invention relates to synthetic plastic drain pipe in the form of continuous pipe having regions or intervals wherein there are pipe openings, said pipe being characterized by other regions free of openings whereby synthetic plastic pipe of such nature an be employed to remove surface waters and the like wherein free flow of water is maintained through the openings. This invention is also directed to an apparatus for producing types of pipe of the above described nature.
2. Discussion of the Prior Art
It has long been the practice to use burned clay pipes which are about 30 cm long and are laid end to end to permit water to enter the pipe through the gaps at the joints and to be carried away inside the pipe. Naturally, the laying of these clay pipes is a time consuming and wearying operation.
In the course of the last 14 or 15 years, synthetic plastic pipes having transverse corrugations containing cut or punched holes have been more widely introduced. These drain pipes which are supplied in considerable lengths can be mechanically laid without undue waste of time and effort.
However, it has been found that in some soils, particularly soils of a sandy or gravelly nature, the effectiveness of such drain pipes diminishes rapidly. This is due to the fact that the fine particles in the soil accumulate at the water entry openings and eventually obstruct or completely choke them.
A method for obviating this undesirable result is known wherein the openings are covered with a filtering material. However, the effect of the filter-jacketed pipes has been found to deteriorate after a period of time, e.g., two years. While it is not known exactly why the filtering material's effectiveness diminishes, experts in the field believe that this circumstance may be due to the fact that in clay pipes entry of the water is confined to a few specific locations, so that the flow rates of the entering water are higher in a clay pipe than in a synthetic plastic pipe where the water entry openings are uniformly distributed along the pipe length. It is thought that the higher rates of flow keep the entry openings clean.
In order to enable clay pipes to be laid by mechanical means, it has been proposed to join them together with coupling sleeves containing water entry openings, the sleeves being sufficiently flexible to permit consecutive pipe lengths to be laid in polygonal traces. Such a suggestion is found in German Pat. No. 1,298,457. Although this permits the pipes to be laid by machines, there are still various objections. Clay pipes are quite brittle and fragile and necessarily must be connected together bearing in mind these limitations.
It is an object of the present invention, therefore, to provide a drain pipe which combines the advantages of the transversely corrugated pipe, which can be manufactured in considerable lengths and mechanically laid without requiring the additional work of fitting coupling sleeves or the like, which pipe has the advantages of clay pipes by providing for the water entry openings to be kept effectively open and clean.